Jim Yanik wrote:
Jeff Liebermann wrote in
:

On Sun, 14 Aug 2011 02:18:37 -0700, mike wrote:

This isn't a problem if you're charging at a fairly low rate. A
good-quality cell -- nicad or NiMH -- will tolerate an indefinite
low ("trickle") charge.

I'd like to see a reference that supports that.

http://batteryuniversity.com/learn/a...l_metal_hydrid

"It is difficult, if not impossible, to slow-charge a NiMH
battery. At a C-rate of 0.1 to 0.3C, the voltage and temperature
profiles fail to exhibit defined characteristics to measure the
full-charge state accurately and the charger must depend on a
timer. Harmful overcharge will occur if a fixed timer controls the
charge. This is especially apparent when charging partially or
fully charged batteries."
Not exactly what you wanted, but a good reason why a "trickle" or
"maintaining" charge doesn't really work.

NiCd batteries are very tolerant of trickle charging.

Nope. I've successfully killed NiCd batteries in (Jedi series) radio
chargers that produce a 0.1c "maintaining" charge when fully charged.
After about a year of continuous charging at 0.1c, the batteries were
all dead. That's what happened to the local hospital emergency
network. The county issued MT2000 radios and chargers to all the
hospitals in the county. In case of emergency, they could all
communicate with each other through a repeater or directly. Once a
week, there was a test to make sure things were working. No problems
for 3 years until I decided to check the batteries. I found a mix of
NiCd and NiMH batteries. All that I tested were dead. The radios
would work for about 2 minutes, which was just long enough for the
test but not long enough for useful operation. Since the batteries
were never discharged, I concluded that the 0.1c maintaining charge
was the culprit.


OTOH,the B&D Dustbuster I had was designed to stay on the charger when not
in use,and it lasted 10 years before I had to have another NiCd pack
installed. that new pack lasted almost as long.
I've seen NiCds listed at DigiKey specifically intended for staying on the
trickle charger when not in use.


Never got any long use like that with several I used. My current red devil
extreme, I only charge it once in a while, and is doing great so far. It is
never without some reserve power left? One Dustbusters I converted to NiMH,
and was a disaster.


Greg